New to SodasStream

I got a SodaStream terra for Christmas and was wanting some flavor suggestions, I typically use Torani syrups when making flavored lemonades and the flavor combo I tried yesterday with my sodastream was pretty good. I love rootbeer and I was wondering, is it more cost effective to get the sodastream flavors or get something like Torani syrups or even just making my own with some extract. Also is there any purpose of getting the metal bottle other than you can carbonate the water in there vs pouring it into an insulated bottle?